Type 'A' and press Enter.

Tech Support: "Type 'A' and press Enter."
Customer: "Didn't work."
Tech Support: "What did it do?"
Customer: "Nothing."
Tech Support: "Hmmm...I'll send you a new set of diskettes."

The problem happened again.
Tech Support: "Hmmm...send me the diskettes back."

They ran perfectly on my machine. I had her print her config.sys and autoexec.bat files, etc. No problems. I called her back.
Tech Support: "Type 'A' and press Enter."

In the background, faintly, I heard these "tickety-tickety" sounds.
Tech Support: "What are you doing?"

It turned out she was typing, "Type A and press Enter." The error message at the bottom of the screen apparently didn't count as "doing anything."